The misfolding of normal proteins has emerged as an important mechanism in both mammalian disease as well as the epigenetic transmission of some phenotypes in lower eukaryotes. The proteins implicated in these phenomena, collectively known as amyloidoses, share a key common trait: the capacity to self-replicate the aberrant fold. Conformational self-replication is a multistep process in vivo, consisting of three highly regulated steps: conversion, maintenance and propagation. While some aspects of this process can be modeled in a simplified system in vitro, a full understanding of the physiological consequences of self-propagating conformations requires an understanding of this pathway in vivo, where basic cellular processes can intersect with and regulate protein dynamics. One particularly intriguing but largely uncharacterized interaction is the relationship between amyloid-forming proteins and the cellular cytoskeleton, which are repeatedly linked together in many systems by a growing series of studies. The overall goal of the work proposed here is to understand the functional interplay between these two systems. Toward this end, my work will focus on prion propagation in lower eukaryotes, which provides an experimentally tractable model for studying the regulation of protein self-propagation in vivo. The Sup35 protein of S. cerevisiae, a protein whose normal function is reversibly modulated by a prion cycle, will be used to examine how actin dynamics influence misfolded protein self-replication. As is the case for a number of mammalian amyloidogenic proteins that have been shown to promote actin bundling, previous studies on the Sup35 prion have identified multiple interactions with proteins associated with the actin cytoskeleton. Through a combination of biochemical, cell biological, and genetic approaches, I will dissect the role of the actin cytoskeleton in the multistep, self-propagation cycle of the Sup35 prion ([PS/"*]) phenotype. As the yeast prion model has been shown to be directly applicable to disorders in higher eukaryotes including a range of human diseases, the insights gained here will provide mechanistic clues into the role of actin in the perpetuation of mammalian protein folding disorders on a molecular level.